1. Field of the Invention
The present invention relates to the field of measuring apparatuses in distribution systems, and particularly to a measuring apparatus allowing for measuring presence and position of an object placed on a carrier as well as a method for such measuring.
2. Description of the Related Art
In large sorting and distribution systems a large number of objects are handled automatically, e.g. sorting of packages in postage systems or handling of parts in re-distribution centrals. Typically the objects are loaded onto a carrier which transports the objects to a determined location where they are loaded off the carrier. In these types of systems it is important to know the presence, position and shape of objects on the carriers. The presence is required to determine if any objects can be placed onto the carrier prior to loading the object on the carrier or to detect that the object really is placed on a specific carrier. Position is required to adjust cross-belt carrier position to keep the object safely within the carrier or to calculate the optimum extraction position. Two-dimensional and/or three-dimensional shape is required in e.g. a package distribution system, where there is a need to calculate volume based freight costs and/or optimum loading on e.g. a truck.
The objects to be handled in such sorting and distribution systems can be of very different sizes and materials, and may be wrapped in clear plastics etc. This makes the detection/measuring of presence, position and shape of objects difficult with simple techniques.
A commonly used technique for sensing that an object is present on a carrier is the use of a simple light switch, such as a photo sensor, which can detect presence and position information in at least one dimension along the carriers' direction of movement. However, a problem associated with this technique is that it is nearly impossible for the sensor to sense an object which is low in relation to the vertical vibration of the carriers and the technique can only be used for systems that use carriers which are flat-shaped. Also, the sensor is not able to detect the position of the object in a transversal direction across the carrier.
Another commonly used technique for sensing that an object is present on a carrier is conventional two-dimensional (2D) image processing. This is made with a standard two-dimensional camera taking a snapshot of the carrier, or a line-scan sensor acquiring the 2D image information as the carrier moves through the Field-of-View (FoV). If the carriers are free from disturbing artifacts, such as paint or stickers, two-dimensional image processing can typically extract 2D-position and shape of objects. However, typically the carriers will be stained with e.g. stickers after being used for a while, which makes it hard to extract the needed information using 2D image processing. Additionally, using 2D image processing is very hard when the color of the object is similar to the color of the background, i.e. the carrier.
Still another used technique for sensing that an object is present on a carrier is a three-dimensional (3D) image processing. When using 3D data most objects are detected securely. However, for certain materials the 3D image acquisition might give no secure 3D information, such if the objects are very reflective, very dark or very low in height.
Many of the systems existing today, described above, used for these types of measurements of objects are only capable of handling carriers having a flat form but often there is a requirement for the use of carriers with different shapes, for example flat carriers with edges and bowl-shaped carriers. It is also desirable to be able to do the measuring of the objects even if the carrier is vibrating or if it for any reason is tilted with reference to the nominal alignment.
One prior art approach is disclosed in U.S. Pat. No. 6,102,291, in which an apparatus detects the presence and position of an object on a bearing surface of a moving supply plane. The measuring is made with a modulated light laser scanner that is placed above the supply plane. The apparatus is first of all used for the reading of optical codes (bar codes) positioned on the surface of the object.
However, in this prior art approach the measuring is done with a modulated time-of-flight laser scanner. The modulated light laser scanner has movable parts which causes wear and it also requires regular maintenance. Also, when a high level of 3D accuracy is needed the use of a modulated light laser scanner becomes very expensive.
Although the known prior art solves some of the problems described above it does not specifically address the problem of non-flat carriers and the problem of providing measurement for very small objects or objects having similar color as the background color.
Thus, an object of the present invention is to provide an improved apparatus and method that enables for the use of non-flat carriers and for the measuring of very small objects or objects having similar color as the background color,